1. Field of the Invention
This invention relates to apparatus for removing a portion of a buffer tube used in a loose tube type of optical fiber cable in order to selectively access an optical fiber found therein.
2. Description of the Prior Art
The use of optical fibers in telephonic and other communication is well-known in the prior art. In order to protect the delicate optical fibers and to facilitate the laying of optical fibers it is well-known to loosely dispose a number of fibers in a buffer tube.
In a known cable assembly, several buffer tubes are wrapped around a central elongate strength or support member and the resultant structure is encased within a common protective sheath of steel and plastic material such as polyethylene, polyurethane, polyvinylchloride, etc. The interior of the cable, between buffer tubes, is filled with a resin or oil-like substance providing lubrication and water resistance. The interior of the buffer tubes is usually filled with a gel which surrounds the individual optical fibers thereby providing lubrication, water resistance, and a light barrier between optical fibers for preventing interference between the fibers.
A design in which one or more optical fibers are loosely disposed in a buffer tube so as to "float" within the gel enclosed therein may be referred to as a loose buffer tube design. Typical variations of the aforementioned design may be found in U.S. Pat. Nos. 4,072,398; 4,143,942; 4,153,332 and 4,230,395.
While optical fibers have many advantages, such as high density and lack of electromagnetic interference, over traditional conducting cable in the communications field, they have a major disadvantage in that there is degradation in transmission efficiency after a fiber has been spliced or in anyway joined with another fiber after the original manufacture. Such a splice may be inevitable in the event of fiber breakage, the rerouting of a communications line or the insertion of an intermediate device within the communications line. However, such a splice may only be required for a single or limited number of fibers within the cable or buffer tube. Under such circumstances, it would be extremely time consuming and degrading to the communication efficiency to completely sever and subsequently splice all the optical fibers in a cable or buffer tube in order to access a single optical fiber. It would therefore be advantageous to provide a device which could allow access to a limited number of fibers within a fiber optic cable without cutting or otherwise disturbing the remaining optical fibers.
Siecor Corporation manufactures Optical Fiber Access Tool (OFT-000) which consists of two subassemblies hinged to one another. Each subassembly includes two open wedge-shaped channels, disposed parallel to the longitudinal axis of the device. The open channels are positioned so that when the subassemblies are folded against one another, two closed channels of a diamond cross-section are formed therebetween. Each channel is of a different size corresponding to sizes commonly used in the manufacture of buffer tubes.
Each of the open channels includes a blade disposed parallel to its longitudinal axis. The blade is seated so as to extend into the center of the channel.
In order to access an optical fiber, the buffer tube is placed into an open channel of an appropriate size and the subassemblies are folded against one another thereby enclosing the buffer tube. As the buffer tube is enclosed, two blades, one blade from each subassembly, are driven into the buffer tube. The user then draws the tool parallel to the longitudinal axis of the buffer tube thereby cutting the buffer tube in two and exposing the optical fibers. The two halves of the buffer tube are then removed leaving all fibers totally exposed and unprotected.
The Siecor device exhibited several disadvantages. The buffer tube is cut by two blades each extending to the center of the tube resulting in a more intrusive device than is sometimes necessary. Such intrusion may result in unwanted nicking or severing of an optical fiber. Since the tool is very large, the buffer tube must be withdrawn a significant distance from the cable in order to fit the tool around the buffer tube. This presents considerable difficulty when attempting to use the tool with a cable whose buffer tubes are helically wound and are not provided with a large amount of slack. Indeed, the Siecor device is particularly designed for a cable having buffer tubes with a reverse helical lay so that the buffer tubes have significant slack when a length of sheathing is removed.
A loose, improperly seated, or dirty blade could extend even further into the buffer tube thereby causing even more damage to the optical fibers. As the cutting process is hidden from view by the folded subassemblies, the user is not able to monitor the cutting process and stop in the event of malfunction. Finally, the device, in its open position, presents four exposed blades thereby creating a hazard to the user.